James Gandolfini plays the C.I.A. director in "Zero Dark Thirty," directed by Kathryn Bigelow. Mark Boal won the prize for original screenplay awarded by the Writers Guild of America. AP Photo | Columbia Pictures

The guild’s adapted screenplay award Sunday went to Chris Terrio for “Argo,” director Ben Affleck’s tale of the CIA’s daring masquerade of six U.S. diplomats as a Hollywood film crew to rescue them from Iran during the hostage crisis there.

Mark Boal won the prize for original screenplay for “Zero Dark Thirty,” director Kathryn Bigelow’s chronicle of the CIA’s manhunt for al-Qaeda leader Osama bin Laden.

Director Malik Bendjelloul won the documentary award for “Searching for Sugar Man,” his portrait of acclaimed but largely forgotten 1970s musician Rodriguez.

The guild was the last of Hollywood’s major trade unions to weigh in on the year’s top films before next Sunday’s Academy Awards.

“Argo” has emerged as the best-picture favorite for the Oscars after sweeping top prizes at earlier film honors, including the Golden Globes and awards from the Directors Guild of America, the Screen Actors Guild and the Producers Guild of America.